A vertical insulated gate transistor is a device that overcomes many limitations of a planar MOS transistor, particularly those with lengths less than 0.1 micron. The channel region of a vertical transistor is formed in a silicon pillar that has gate insulator and a gate on its sides. The vertical insulated gate transistor is a technological platform that is particularly suitable for implementing a coating gate architecture with ultra short dimensions, because the channel length in the vertical insulated gate transistor is not fixed by the photolithographic resolution as it is with a planar MOS transistor. It is therefore possible to form channels in a vertical transistor with very small dimensions using standard photolithographic equipment. Also, coating a projecting silicon pillar with a gate is much simpler than coating a thin silicon film buried in a substrate, as is found in planar MOS transistors.
Vertical transistors have a single substrate that acts as the source. One exemplary vertical transistor is described in commonly assigned U.S. Pat. No. 6,746,923, which is incorporated herein by reference. This patent describes a method of fabricating a vertical quadruple conductive channel insulated gate transistor. The resulting structure may not have a source region that is electrically isolated from the substrate, depending on the conductivity types of the source and the substrate. If the substrate is p-type (or if the substrate contains a p-type well) and the source is n-type (or vice versa), the structure is compatible with most circuits.
However, there are other applications in which it is desirable to have the source and the body of the transistor electrically isolated. This is particularly true with stacked devices, such as totem pole or H-bridge transistor configurations, because isolation between components in a circuit is both advantageous and desired. For instance, stacked devices with source and body electrically isolated are better suited for high-frequency analog applications and applications in which electromagnetic pulses (EMPs), which are broadband, high-intensity, short-duration bursts of electromagnetic energy, are anticipated. Another example of applications in which immunity between communication channels is important is in photo-detector applications.